The invention refers to a chain for a flight conveyor, the chain consisting of individual chain links connected with each other by means of hinge bolts, a flight attachment being fixedly arranged on the two sides of the chain links and disposed at least in part in a plane parallel to the respective hinge bolt, said flight attachment being provided with a rest surface for engaging the conveyor trough and connected with another flight attachment by way of a cross piece bridging the chain.
An important problem arising in connection with flight conveyors relates to the wear of the conveyor trough itself. This wear is not uniformly distributed over the entire length of the trough, but tends to arise at particular locations more intensely such as in curved areas. As soon as this wear has attained at these locations its maximum allowable limits, the entire trough must be replaced because of the few places showing too much wear. This causes appreciable costs, on the one hand, and increased down-time, on the other.
It has been proposed in the past (see German Pat. No. 848 029) for this reason to design the trough of individual sections connected with each other, so that wear in any one location would require only one section to be replaced, thus to save money and time. However, this approach did not solve the basic problem of wear.
Other proposals aiming at building the trough at least in part of wear resistant synthetic plastics, such as polyethylene, got closer to the desired results (see U.S. Pat. No. 3,130,708). However, the individual sections of a trough cannot be made too small for reasons of stability. Thus, the problem under discussion failed to get resolved, since the wear at a single location would require a relatively large section to be replaced. Furthermore, such large sections cannot be made of a plastic material, and in particular so polyethylene, in a simple and low cost process, such as molding.
It has been proposed for belt conveyors to vulcanize flight attachments made of rubber onto the belt (see U.S. Pat. No. 3,147, 850). This form of connection evidently is not feasible in the case of chain conveyors. On the other hand, U.S. Pat. No. 2,779,454 discloses chain links provided with reinforcing discs facing each other and having a plastic ring fixedly held therebetween and serving as sealing ring with respect to the trough wall. These sealing rings were made to protrude only a small amount beyond the discs that held them, so that they had to be replaced after a comparatively short time of operation. Otherwise said discs would abrade past the trough.
In another method the problem of wear was to be solved by means of relatively small dimensioned plastics parts manufacturable at low cost. A design having flight attachments of metal provided with shoes of a plastic material has actually been put on the market and proved commercially successful. This solution, however, implied extra effort and expenditures. In addition to the customary flight attachments made of metal, it was necessary to fabricate and mount the plastics shoes in separate operations.
For this reason a new attempt to solve the above problem was made of late. More specifically, a new conveyor chain was put on the market, provided with lateral flight attachments fully made of plastics and fixedly screwed onto the chain fork. For this purpose the flight attachments were each provided with a sharply bent foot having bores penetrated by a pair of fastening screws screwed into threaded holes of the chain fork. Polyethylene was used here too as synthetic plastic. In addition to providing for low friction this solution offered the advantage of lower chain weight. However, the chain links were made weaker by the threaded holes exactly in a location, in which they were particularly stressed. As a consequence, this weakening effect had to be compensated for by overdimensioning the chain links, which more than offset the advantages referred to above. In addition, the sharply bent and relatively short foot ended up being subjected to relatively large torsional moments and stresses readily causing failures in operation.